Author Archive
Yet more transceiver modules!
February 5th, 2015 | 
Author: A search on eBay has thrown up lots of useful RF transceiver modules, not as low cost as the AM ones found by G6ALB, but nonetheless very low cost and suitable for local communications, Some are 100mW and some 500mW or 1W. The ones I saw were data units, but these should be suitable for speech with simple mods. I am unclear how some of these are programmed to the correct frequency. There is usually a choice of either VHF or UHF and I think some are essentially FM.
Put “UHF transceiver module eBay” into Google to see what comes up. Or try “VHF” instead of UHF. I was amazed how low cost these were.
More useful modules
Yet again, I am indebted to Steve G1KQH for the following:
Low cost AM modules yesterday, now the Dorji today.. Its just never ending what next comes along, I can’t keep up any longer going to have a funny turn!73 Steve
http://www.g1kqh.talktalk.net/
70cm AM test with low cost modules
This evening I listened for G6ALB on 70cm. Andrew is 3km from me. We both have V2000 vertical co-linear antennas. He was using a very low cost SAW locked TX module, which produced as much FM as AM when modulated with an electret mic. The biggest problem was Andrew’s low power and low level of modulation. He needs more mic gain, more TX power (10dB more?) and some pre-emphasis on the audio. TX power today was very low milliwatts. From 433.925MHz up to at least 433.990MHz a lot of squeaks and whistles could be heard, presumably from more local ISM devices. I was receiving G6ALB using an FT817 at about RS41 on FM and weaker on AM. This very initial test produced results that were expected. To use a super-regen module on RX (the intention is a very simple AM voice transceiver) will require G6ALB to be considerably stronger than on these first tests.
Another G1KQH bargain
This came in from Steve, G1KQH, today. It is often cheaper to buy the completed, built modules from China than to buy the parts in the UK! What is the world coming to?
I bought 5 LM317s on PCB with heatsinks for a fiver:
Why bother building it any longer, that used to be half the fun! The heatsinks would of cost a Quid each over here, never mind the LM317 and the PCB with connectors..Happy days73 Steve G1KQH
Low cost kits
See http://www.aliexpress.com/store/331885 . This website has some very low cost rigs for sale. An example is a 40m Pixie at around $10 post free. You’d be hard pressed to buy the individual parts for less!
UPDATE 1430z: I have just ordered a 40m Pixie kit from them. Should be here in 2 to 3 weeks time. I hope I can manage to build it with my clumsy soldering currently.
UPDATE 2000z: G1KQH has found the same Pixie at an even better price:
Greetings RogerI could of saved you a fiver out of your pension but you had to rush in:73 Steve
http://www.g1kqh.talktalk.net/
Fredbox derivatives
Since my original Fredbox 2m AM design, a number of derivatives have been designed and built around the world. This is what our hobby is all about. Although the original Fredbox worked well and its results surprised me, it was always ripe for further developments, which is healthy. My Sixbox was a 6m version and at some point, when fitter, I’d like to make a simple 10m AM version for local natters.
See https://sites.google.com/site/g3xbmqrp3/vuhf/fredbox for the original Fredbox. Click on the schematic to enlarge. Other derivative ideas are on my website www.g3xbm.co.uk. By the way, it got its name from Fred G8BWI who was a disabled local in the Cambridge area back in the 1970s. Fred was a regular contact and he could talk for hours and hours and hours and hours zzzzzzzzzzz. RIP Fred.
433MHz AM modules – G6ALB progress
G6ALB has reported some progress in his tests using 433MHz AM modules, although it looks like an external linear audio transistor stage may be necessary to get best AM (voice) sensitivity from the super-regen detector. On TX he is getting 10dBm from the TX module at 5V (more with higher supply voltages) although the mod seems to be a mix of AM and FM. Our first “DX” test will probably be from G6ALB to me using the voice modulated TX module. I’ll receive Andrew on my FT817ND initially. When the super-regen RX is sensitive with speech I’ll try to receive him with that. Super-regens should be sensitive on AM, but are usually poor NBFM detectors. We are about 3km apart and both have V2000 verticals externally mounted. At 70cms these have gain.
Andrew has ordered 5 pairs of 433MHz AM modules (TX as well as RX) for not much more than £2 total from China. This makes each TX/RX pair very inexpensive. It amazes me that they can make these so inexpensively. I hope G6ALB succeeds in this venture. It would be good to be able to communicate with him using a really low cost 70cm transceiver. I expect Andrew will write up his results in an article for a UK magazine later.
It seems entirely possible that a complete 70cm AM transceiver can be made for just a few pounds based on these low cost 433MHz AM modules.
