EMRFD Message Archive 11718

Message Date From Subject
11718 2015-10-03 10:02:44 kg4rll Switching Questions

General question about the best method to use for switching between the front end filters, crystal IF filters, BFO crystals etc.....

What is the best method? Diodes? Relays? Transistors?




11719 2015-10-03 11:07:14 William Martin Re: Switching Questions

I use 12 vdc enclosed dip relays. Simple cheap and reliable. Maybe not the best. I use them for switching oscillators and front end boards in my receiver project.

I looked at using diodes and transistors for switching and it always seemed to increase the complexity of the overall project.

I would be interested in what others have to say. With relays if you have a bad one you just pull it out of the dip socket and put a new one in.

Bill N7EU

  Sent from Bill's iPad 3  
11720 2015-10-03 12:51:31 kb1gmx Re: Switching Questions

What is the best method? Diodes? Relays? Transistors?



The all work and depending on layout and parts used likely about the same.

You have to think about it and test to know.

Its really about style, preferences, power consumption and my favorite

what I have on hand.


11721 2015-10-03 16:59:32 bob_ledoux Re: Switching Questions
EMRFD page 6.62 states that measurements are required to maintain IMD performance when diode switches are used.  PIN type diodes are recommended.

Relays may be simpler.

11725 2015-10-03 20:15:03 kerrypwr Re: Switching Questions
I've used the DIP reed relays to switch filters for a 5 MHz IF; they worked OK.

For interest, I did some tests of insertion loss and isolation;

Insertion loss;



The DUT was a PRMA DPDT in a 14-pin (but with most pins omitted) DIL package.

Kerry VK2TIL.
11730 2015-10-05 09:19:38 atlantaswl Re: Switching Questions
I use 5V enclosed relays for bypass filter switching on the front end, and the same for switching in crystal filters.  Seems to do a good job.  Controlling multiple banks with the MAX4820 relay driver using SPI makes implementation pretty simple.


11731 2015-10-05 09:35:24 Dan Rae Re: Switching Questions
Despite a number of replies in this thread advocating relays, I don't
think anyone has yet pointed out the desirable use of "DC wetting" for
low level signal circuits using relays which has been used in the
telecoms field for many years. Look at the design of the front ends of
pa3ake as well as the CDG2000 transceiver for examples.

Also there is another possibility, that of using FET bus switches, see
the BPF filters in the excellent Pic-A-Star design. Cheap and perform well.

Dan - ac6ao
11732 2015-10-05 09:52:25 Dana Myers Re: Switching Questions
11733 2015-10-05 11:25:05 Dana Myers Re: Switching Questions
11734 2015-10-05 14:23:06 sohosources Re: Switching Questions
Regarding dc whetting:

When building switches for front-end filters, etc, the convenience of relays is high, while the extra parts counts for dc whetting seem to offset that convenience considerably.

I was considering using DIP sockets (for the relays) in my designs (as another posted pointed out), which gives me the option of making an outboard "relay cleaner," which would pass the required dc current through the device while actuating it rapidly (10-50 Hz, depending on relay speed). The idea being to physically and electrically "clean" the internal contacts.

My idea was to remove each relay once or twice a year to "thrash" them in the "relay rejuvinator," thereby eliminating any relay-based performance degradation.

Any thoughts on whether this will work?  :)


--Kirk, NT0Z

My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)
11741 2015-10-06 09:14:58 Mark Dunning Re: Switching Questions

There were commercial relay contact cleaners on the market about 30
years ago that I know about, that passed a current of around 100mA
through the relay's contacts while switching back and forth to clean
them. They seemed to work okay as I recall.

I think it would depend a lot on the contact surface materials. The
relays I am talking about were high quality units with contact ratings
of 5A. I think with small DIP style relays you probably run the risk of
doing more damage, rather than good doing this.

73's Mark VK6WV