EMRFD Message Archive 12544
Message Date From Subject 12544 2016-03-26 11:31:51 va3vfo RF Sweep generator and other test Equip. I have had success repairing RF equipment with a minimum of test equipment (DDM, RF probe etc)
but I am done trying to use outdated RF signal generators (heathkit etc) that is reducing my confidence due to broad harmonics etc...
I am looking for recommendation for a basic, but reliable (and frequency readable) RF generator to test RF front-ends (1Mhz up to vhf if possible...), as well as other recommendations for measuring IF signal strengths etc. I have a frequency counter (radio shack22-006) which needs high RF drive to work ( ok for Xmiters)
I have a HP 608E VHF tube Generator, but it never seemed to work and may not be worth fixing/recapping etc...any thoughts?
.Rather than used, Solid state vintage lab finds,( I am tired of defective, unreliable used gear), and am thinking of a simple, modern kit, or software driven kit...there seems to be so much out there...Just not sure what I want, need or what is realistic in the $200 range.
I am probably all over the map on this...
12545 2016-03-26 11:40:44 Ashhar Farhan Re: RF Sweep generator and other test Equip. try the sweeperino. it has really made life simple for me. i am a changed man. girls like me, etc. etc. people stop me in the streets and take autographs.- f 12546 2016-03-26 13:02:01 K5ESS Re: RF Sweep generator and other test Equip.
The sweeperino is pretty neat but since it has a square wave output you will have harmonics just like the old outdated units you mentioned. For a signal source up to 70 MHz check out the PHSNA Experimenters board with an AD9851. It will give you an SFDR of >40 dB at 70MHz and below. Probably won’t attract women or autograph seekers though. The PHSNA with the AD8307 power meter can provide you with a means of measuring IF signal strengths, insertion loss, return loss, VSWR etc. up to its frequency limit. Here’s a link to the groups site. https://groups.yahoo.com/neo/groups/PHSNA/info You can buy unpopulated boards from Jim, N5IB at least until he sells out. He does re-order periodically.
12547 2016-03-26 14:06:58 kerrypwr Re: RF Sweep generator and other test Equip. Greg specified a " ... basic RF generator ... "; there are quite a few DDS-based generator kits available at reasonable cost.
Ebay is one source but look here;
MiniKits is in Australia but the low A$ means low prices that largely offset the postage cost; Mark VK5EME is very helpful and sends a lot of things overseas.
I built one of the higher-end kits;
but a build need not be this elaborate and the cost will be much lower. You can work it out but you could probably get a basic generator kit for around US$100.
Points to note are;
Firstly, the sweep function is not really usable as there is no trigger output; I built it mainly as a sweeper and was disappointed to discover that there is no trigger output (I did, however, console myself by building an N2PK VNA and a DG8SAQ VNWA which more than made-up for the disappointment :) ).
Secondly, the output spectrum was OK but not particularly "clean"; I traced most of this to the MMIC output amplifier. I removed this and substituted a "strong" 2N5109 amplifier of the kind seen in EMRFD and the output spectrum was greatly improved;
Artefacts of the DDS can be seen but they are well down in amplitude; the harmonic performance was quite good;
The higher harmonics were removed with a 70MHz LPF in the final build.
Thirdly, shielding is not as good as a commercial generator of the HP kind; it's OK, though, with the steel case and PCB-material front panel that I used.
Leakage can just be detected with a probe held close to the front panel (which has cutouts for switches etc; about -70dBm can be detected.
This is fine for most purposes.
Fourthly, there is no output attenuator; an external one is required. I have a range of attenuators;
which address that factor.
Greg also sought " ... recommendations for measuring IF signal strengths etc ... "; the AD8307 power meter is ideal for this.
I built one based on Bob Kopski's dual-meter design and it was the best single instrument that I ever built.
If I were building one again I would just buy this kit with two probes;
Again, it's in Australia, but I think you would be hard-pressed to buy the parts at that price and, knowing the seller, the kit will be first-class. There is a lot of very interesting information on the site.
12548 2016-03-26 18:48:21 kerrypwr Re: RF Sweep generator and other test Equip. I inserted a wrong link in my previous message; this is the output of the DDS generator;
It's pretty good; undesirable outputs are quite low.
It's instructive, though, to compare it with a similar output from my HP8657B;
That, I suppose, is one of the many reasons that good signal generators are expensive!
12549 2016-03-26 18:54:50 John Re: RF Sweep generator and other test Equip. To test RF front ends, I assume you need accurate low level signals.
Probably AM and FM modulation also. There are lots of neat digital
projects which produce very accurate and easily controllable frequency
signals, but they are high level outputs. To put these in a box with
enough shielding would be a major, major effort.
For example, I could receive my Heathkit Laboratory Signal Generator
from across the room without a coax between them, and it was built with
a copper plated box inside another one. No way to measure 1 uV receiver
sensitivity. Take a look inside your HP608 to see the metal required
for low leakage.
Look for one from a local seller where you can check it out first and
it's not likely to fail for years.
12550 2016-03-26 19:15:25 va3vfo Re: RF Sweep generator and other test Equip. Thanks to all for your replies...exactly the kind of information I was looking for...I will read up on all the recommendations, and digest...
One unit that I considered is the Elecraft XG-3 RF Signal Source.. At the high price end ( with the US/CDN exchange) and certainly not as flexible as some of the other software driven devices- but have heard its a good unit.
I had looked at some of the devices mentioned, so glad I am in the ball park...I will likely be back with follow up questions..
12551 2016-03-26 20:38:31 Ashhar Farhan Re: RF Sweep generator and other test Equip. There are no generators without any harmonic outputs at all. Every generator will show outputs at harmonics. this is something that you will have to live with. one simlpe way, though not the most efficient is to have a bank of low pass filters (just like the venerable HP8640B) that will keep the harmonics down (but not out).The other thing to do (which I do) is to keep your sweeps within one harmonic (Let's say you sweep the 7 MHz BPF from 5 to 55 MHz, this way you avoid the second harmonic of 3.5 MHz showing up as a response).the only REAL way out of this is to have a tuned detected as well. That means a spectrum analyzer with a sweep generator. only that will give you the correct, harmonic and spur free sweeps.- f 12552 2016-03-27 09:23:48 mosaicmerc Re: RF Sweep generator and other test Equip. Consider the 250Khz to 250Mhz Tek SG503 as a leveled RF sine wave gen , I have that and an SG504 to go to 1Ghz. They can do 0.5 to 5Vpp sine wave. A typical use for them is in calibrating RF gear and 'Scopes etc.
You can get SG503's (which do not need an remote head) in the $120 to $250 range on Ebay. I got mine for $180 in a 3 slot mainframe a few months ago....works fine and fairly easy to repair/test/cal as Tek supplies full schematcs, operation theory and diagnostic info in the manuals.
Note these 5xx series items are plugins for the Tektronix 5xx series mainframes which are very common & cheap in sizes from 1 to 6 plugin capability. If you're a little lucky you can get a 3 or 4 mainframe plugin unit preloaded with the SG503 & other useful plugins for a good price. Ebay.
I purchased a separate DC505a 225Mhz universal counter & event timer that needed a bit of servicing ( 2 bad digits (LED)) for $65. Turned out to be a loose connector. Now my 3 plugin mainframe has a SG503, SG504 and DC505A for a nice RF sweep gen to 1.05Ghz plus freq counting. All for about $350. All calibrated and working now.
I also make the custom remote leveling head for the SG504 which are hard to find in combo with the original head as the heads get separated being jacked in.
My leveling head is superior ( to the OEM head) in flatness to 1Ghz with the SG504....0.08dB Pk to Pk flatness across the whole range, as each head is custom impedance matched to the BNC connectors used to reduce uncertainty. Each head is tested with a 12.4Ghz Boonton 4210-4b calibrated power meter and a DSA 815 for harmonics. I also did some HP8753D VNA tests on the head for S21 parameters.
As a project I am building a Trimble OCXO 10 MHz ref. with dist. amp to syncmy SA, VNA and the DC505a (which needs a divide by 2 as it uses a 5Mhz ext ref)
12553 2016-03-28 10:12:30 winston376 Re: RF Sweep generator and other test Equip. There is no free lunch....
If you want to do some accurate and reliable testing then $ 200 isn't going to cut it. A versatile test instrument for what you're doing is a vector network analyzer and filters.
I wasted hours on using and trying to correlate test data using equipment similar to yours....Heath kit gen, cheap freq counter, graph paper, pencils and erasers, etc. until I purchased this product. Now I routinely test pass bands on filters, S parameters, VSWR, etc in minutes. It also can be used as a spectrum analyzer and accurate oscillator.
There is also the associated yahoo support group: DG8SAQ VNWA users group you can join for help.
VNWA 3 Product information:
12554 2016-03-30 18:38:14 kx4om Re: RF Sweep generator and other test Equip. You can probably do a lot what you need to do in RF testing in a 50-ohm system for a lot less cost than a spectrum analyzer or VNA.
Many on the forum are familiar with this, but for others, check out the PHSNA Yahoo group (PHSNA is the acronym for "Poor Ham's Scalar Network Analyzer". N5IB and W5JH put this idea into production, with software work by WA5BDU.
The SNA uses PC control (via a custom no-cost Windows program by WA5BDU, or an Excel spreadsheet or terminal program as alternatives) of an Arduino-SNA-DDS signal generator board stack, with the output from what you are sweeping fed through a logarithmic power detector (based on the W7ZOI-W7PUA article from QST Dec. 2001.) The analog DC voltage output from the log power meter is fed to the input of the SNA. Sweep an L-C filter, a crystal filter, a crystal by itself, and even an antenna. You get the raw data as well as a Bode plot. They can be saved as files.
An add-on, should you need it, is a measurement receiver, designed as part of the group's tool set by W5JH. It is a superhet, with the SNA providing the LO, and it features attenuators, amplifiers, a diode ring mixer, a diplexer, a 6-stage 400 Hz bandwidth crystal filter and matching networks for the 50-ohm system. The windows software includes functionality for the measurement receiver.
The details on all of the above are on the PHSNA group. Schematics, build details, software, examples of builds and modifications, and possibly even the PC boards, which are ordered in group buys a couple of times a year, based on past history. The highest cost items are the AD8307 log amp IC, an Ardunio Uno clone and eBay Chinese DDS board, and the ADE-1 for the mixer, an ERA-3+ MMIC (free sample from manufacturer recommended) and a lot of 15 or so crystals from which to select 6 for the measurement receiver. Probably less than $100 for the whole shebang, if you like to build kits; even lower if you like to build from schematics.
12555 2016-03-30 19:18:48 Gary Winblad Re: RF Sweep generator and other test Equip. Absolutely, if you are on a budget like me and do any kind of RF work, BUILD a PHSNA!
Next to my scope, it is the most valuable thing on my bench. The only thing that can
come close is Elsie program.. because its free.
Cost is cheap if you use ebay chinese vendors, everything I got was good quality.
AD8307 log amps were something like 5 for $5 shipped :)
I easily modified mine with an LCD display and a rotary encoder and programming to
make it into a bench RF sweep generator. Now I can easily align filters with my scope
in real-time. Then I can use WA5BDU's Windows program to make beautiful plots to